Contact lenses have been utilized for many years for the correction of various visual disorders. However, contact lenses have been less successful in the treatment of presbyopia. Presbyopia is characterized by loss of elasticity of the crystalline lens, and hence, loss of the ability of the eye to adjust to clearly see objects which are close and also those which are more distant.
Two common methods for correcting presbyopia are the use of bifocal eyeglass lenses and bifocal contact lenses. Eyeglass lenses generally have two portions ground for two viewing distances. Since the eye will move in relation to the lens, the patient can easily view through either lens.
Two types of multi-focal contact lenses are presently known. One type is quite similar to eyeglasses, in that it moves relative to the eye in order to place the correct portion of the lens over the pupil for viewing. Such lenses are generally categorized as translating lenses; one such lens being described in U.S. Pat. No. 4,418,991 to Breger. These lenses have a lower portion which is engaged by the lower eyelid when the patient looks down, causing the lens to move upwards on the cornea relative to the pupil. Translating lenses are difficult to fit because the amount of movement of the lens will vary for each patient, making it difficult to determine the appropriate height of the bifocal segment.
Soft contact lenses are typically of a diameter large enough to extend beyond the cornea and into the scleral area. A thick peripheral portion fits into the natural notch created in the limbal area where the flatter scleral meets the steeper cornea. Such lenses can be of the translating type (described above), or of the simultaneous type. Simultaneous type of lenses, one being described in U.S. Pat. No. 4,199,231 to Evans, utilize a lens which does not move on the cornea, but rather causes the light rays to focus within a specific range forward and behind the retina. Such lenses require an increase in the distance prescription power for normal distance viewing in order to bring the near vision focal point within an acceptable range. This, in affect, will slightly blur the distance vision, since the focal point will be moved from the retina to a point slightly beyond the retina. Obviously, it is much more desirable to have the focal point of light rays from an object at any distance to be focused directly on the retina, and not merely within an "acceptable range" of the retina.
It is therefore an object of the present invention to provide an improved variable power contact lens.
Another object is to provide a variable power contact lens which is neither translational nor simultaneous and therefore suffers none of the problems associated with those lenses.
Yet another object of the present invention is to provide a contact lens which will provide a variety of focal lengths through the same portion of the lens.
These and other objects will be apparent to those skilled in the art.